This invention generally relates to a syringe assembly having a needle sheath.
Increasingly, medicaments are supplied from manufacturers in prefilled syringe assemblies. Such assemblies include a syringe that has a needle cannula and is filled with the medicament. Typically, a needle sheath covers the needle cannula to prevent accidental contact with the needle. Manufacturers supply such syringe assemblies as prepackaged, sterile, single use units. Thus, it is necessary to create a syringe assembly than can be sterilized after the needle sheath is placed over the needle cannula.
In the past, needle sheaths were primarily composed of rubber. With the advent of modern thermoplastic elastomers, many manufacturers have switched to thermoplastic elastomers as the material of choice for needle sheaths. Thermoplastic elastomers offer the advantages of being: cleaner than natural rubber products; providing better dimensional control of parts; available in a wider variety of synthetic materials to insure compatibility with a particular medicament; lower cost than natural rubber; and reduced leeching of materials from the needle sheath into the medicament.
Thermoplastic elastomers also permit a wider choice of sterilization methods between gases like ethylene oxide, irradiation, or autoclaving. One problem with some synthetic thermoplastic elastomers is that the particular composition which is most compatible with a particular medicament has a low permeability to a sterilizing gas.
Thus, it is desirable to provide a needle sheath that can be sterilized using any sterilizing gas while permitting the needle sheath to be composed of any thermoplastic elastomer, including one having a low permeability to the particular sterilizing gas. In addition, it is sometimes desirable to produce a needle sheath formed of plastic. Plastics generally have low gas permneability. Thus, it is desirable to provide a needle sheath that can be formed of materials with low gas permeability and still be sterilized by a sterilizing gas.
In general terms, this invention provides a syringe assembly having a needle sheath that can be formed of a material having a low gas permeability, but which can be sterilized using a sterilizing gas.
A syringe assembly designed according to this invention includes a syringe body, a needle cannula, and a needle sheath. The needle sheath has a body portion with a cavity that is open at a first end and closed at a second end opposite the first end. The cavity receives the needle cannula and includes a passage in communication with the first end of the cavity. The passage has a shape that permits gas from the external atmosphere to flow into the cavity while simultaneously preventing entry of microorganisms from the external atmosphere into the cavity.
These and other features and advantages of this invention will become more apparent to those skilled in the art from the following detailed description of the presently preferred embodiment. The drawings that accompany the detailed description can be described as follows.